Magnetic junctions using asymmetric free layers and suitable for use in spin transfer torque memories

ABSTRACT

A magnetic junction usable in a magnetic device is described. The magnetic junction includes a pinned layer, a nonmagnetic spacer layer, an asymmetric free layer and a perpendicular magnetic anisotropy (PMA) inducing layer. The nonmagnetic spacer layer is between the pinned layer and the free layer. The free layer is between the nonmagnetic spacer layer and the PMA inducing layer. The asymmetric free layer includes a first ferromagnetic layer having a first boron content and a second ferromagnetic layer having a second boron content. The second boron content is less than the first boron content. The first boron content and the second boron content are each greater than zero atomic percent. The magnetic junction is configured such that the asymmetric free layer is switchable between stable magnetic states when a write current is passed through the magnetic junction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional Patent ApplicationSer. No. 62/020,929, filed Jul. 3, 2014, entitled ASYMMETRICAL FREELAYER FOR PERPENDICULAR MTJ, assigned to the assignee of the presentapplication, and incorporated herein by reference.

BACKGROUND OF THE INVENTION

Magnetic memories, particularly magnetic random access memories (MRAMs),have drawn increasing interest due to their potential for highread/write speed, excellent endurance, non-volatility and low powerconsumption during operation. An MRAM can store information utilizingmagnetic materials as an information recording medium. One type of MRAMis a spin transfer torque random access memory (STT-MRAM). STT-MRAMutilizes magnetic junctions written at least in part by a current driventhrough the magnetic junction. A spin polarized current driven throughthe magnetic junction exerts a spin torque on the magnetic moments inthe magnetic junction. As a result, layer(s) having magnetic momentsthat are responsive to the spin torque may be switched to a desiredstate.

For example, FIG. 1 depicts a conventional magnetic tunneling junction(MTJ) 10 as it may be used in a conventional STT-MRAM. The conventionalMTJ 10 typically resides on a bottom contact 11, uses conventional seedlayer(s) 12 and includes a conventional antiferromagnetic (AFM) layer14, a conventional pinned layer 16, a conventional tunneling barrierlayer 18, a conventional free layer 20, and a conventional capping layer22. Also shown is top contact 24. Conventional contacts 11 and 24 areused in driving the current in a current-perpendicular-to-plane (CPP)direction, or along the z-axis as shown in FIG. 1. The conventional seedlayer(s) 12 are typically utilized to aid in the growth of subsequentlayers, such as the AFM layer 14, having a desired crystal structure.The conventional tunneling barrier layer 18 is nonmagnetic and is, forexample, a thin insulator such as MgO.

The conventional pinned layer 16 and the conventional free layer 20 aremagnetic. The magnetization 17 of the conventional pinned layer 16 isfixed, or pinned, in a particular direction, typically by anexchange-bias interaction with the AFM layer 14. Other versions of theconventional MTJ 10 might include an additional pinned layer (not shown)separated from the free layer 20 by an additional nonmagnetic barrier orconductive layer (not shown). The conventional free layer 20 has achangeable magnetization 21. Although shown as in-plane, themagnetization 21 of the conventional free layer 20 may have aperpendicular anisotropy. In some cases, the pinned layer 16 and freelayer 20 may have their magnetizations 17 and 21, respectively orientedperpendicular to the plane of the layers. For example, for thicknesseson order of twelve Angstroms or less, the free layer 20 including CoFeBmay have its magnetic moment oriented perpendicular to plane. However,for higher thicknesses, the free layer magnetic moment is generally inplane.

To switch the magnetization 21 of the conventional free layer 20, acurrent is driven perpendicular to plane (in the z-direction). When asufficient current is driven from the top contact 24 to the bottomcontact 11, the magnetization 21 of the conventional free layer 20 mayswitch to be parallel to the magnetization 17 of the conventional pinnedlayer 16. When a sufficient current is driven from the bottom contact 11to the top contact 24, the magnetization 21 of the free layer may switchto be antiparallel to that of the pinned layer 16. The differences inmagnetic configurations correspond to different magnetoresistances andthus different logical states (e.g. a logical “0” and a logical “1”) ofthe conventional MTJ 10.

Because of their potential for use in a variety of applications,research in magnetic memories is ongoing. For example, mechanisms forimproving the performance of STT-RAM are desired. Accordingly, what isneeded is a method and system that may improve the performance of thespin transfer torque based memories. The method and system describedherein address such a need.

BRIEF SUMMARY OF THE INVENTION

A magnetic junction usable in a magnetic device is described. Themagnetic junction includes a pinned layer, a nonmagnetic spacer layer,an asymmetric free layer and a perpendicular magnetic anisotropy (PMA)inducing layer. The nonmagnetic spacer layer is between the pinned layerand the free layer. The free layer is between the nonmagnetic spacerlayer and the PMA inducing layer. The asymmetric free layer includes afirst ferromagnetic layer having a first boron content and a secondferromagnetic layer having a second boron content. The second boroncontent is less than the first boron content. The first boron contentand the second boron content are each greater than zero atomic percent.The magnetic junction is configured such that the free layer isswitchable between stable magnetic states when a write current is passedthrough the magnetic junction.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a conventional magnetic junction.

FIG. 2 depicts an exemplary embodiment of a magnetic junction usable ina magnetic memory programmable using spin transfer torque and whichincludes an asymmetric free layer.

FIG. 3 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 4 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 5 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 6 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 7 depicts another exemplary embodiment of a magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 8 depicts an exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 9 depicts another exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 10 depicts another exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 11 depicts another exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 12 depicts another exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 13 depicts another exemplary embodiment of a dual magnetic junctionusable in a magnetic memory programmable using spin transfer torque andwhich includes an asymmetric free layer.

FIG. 14 depicts an exemplary embodiment of a memory utilizing magneticjunctions in the memory element(s) of the storage cell(s)

FIG. 15 depicts an exemplary embodiment of a method for providing amagnetic junction usable in a magnetic memory programmable using spintransfer torque and which includes an asymmetric free layer.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments relate to magnetic junctions usable inmagnetic devices, such as magnetic memories, and the devices using suchmagnetic junctions. The following description is presented to enable oneof ordinary skill in the art to make and use the invention and isprovided in the context of a patent application and its requirements.Various modifications to the exemplary embodiments and the genericprinciples and features described herein will be readily apparent. Theexemplary embodiments are mainly described in terms of particularmethods and systems provided in particular implementations. However, themethods and systems will operate effectively in other implementations.Phrases such as “exemplary embodiment”, “one embodiment” and “anotherembodiment” may refer to the same or different embodiments as well as tomultiple embodiments. The embodiments will be described with respect tosystems and/or devices having certain components. However, the systemsand/or devices may include more or less components than those shown, andvariations in the arrangement and type of the components may be madewithout departing from the scope of the invention. The exemplaryembodiments will also be described in the context of particular methodshaving certain steps. However, the method and system operate effectivelyfor other methods having different and/or additional steps and steps indifferent orders that are not inconsistent with the exemplaryembodiments. Thus, the present invention is not intended to be limitedto the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features described herein.

The magnetic junction(s) described herein are usable in magneticdevice(s). For example, the magnetic junction(s) may be within magneticstorage cells for a magnetic memory programmable using spin transfertorque. The magnetic memories may be usable in electronic devices thatmake use of nonvolatile storage. Such electronic devices include but arenot limited to cellular phones, tablets, and other mobile computingdevices. The magnetic junction includes a pinned layer, a nonmagneticspacer layer, an asymmetric free layer and a perpendicular magneticanisotropy (PMA) inducing layer. The nonmagnetic spacer layer is betweenthe pinned layer and the free layer. The free layer is between thenonmagnetic spacer layer and the PMA inducing layer. The asymmetric freelayer includes a first ferromagnetic layer having a first boron contentand a second ferromagnetic layer having a second boron content. Thesecond boron content is less than the first boron content. The firstboron content and the second boron content are each greater than zeroatomic percent. The magnetic junction is configured such that the freelayer is switchable between stable magnetic states when a write currentis passed through the magnetic junction

The exemplary embodiments are described in the context of particularmagnetic junctions and magnetic memories having certain components. Oneof ordinary skill in the art will readily recognize that the presentinvention is consistent with the use of magnetic junctions and magneticmemories having other and/or additional components and/or other featuresnot inconsistent with the present invention. The method and system arealso described in the context of current understanding of the spintransfer phenomenon, of magnetic anisotropy, and other physicalphenomenon. Consequently, one of ordinary skill in the art will readilyrecognize that theoretical explanations of the behavior of the methodand system are made based upon this current understanding of spintransfer, magnetic anisotropy and other physical phenomena. However, themethod and system described herein are not dependent upon a particularphysical explanation. One of ordinary skill in the art will also readilyrecognize that the method and system are described in the context of astructure having a particular relationship to the substrate. However,one of ordinary skill in the art will readily recognize that the methodand system are consistent with other structures. In addition, the methodand system are described in the context of certain layers beingsynthetic and/or simple. However, one of ordinary skill in the art willreadily recognize that the layers could have another structure.Furthermore, the method and system are described in the context ofmagnetic junctions having particular layers. However, one of ordinaryskill in the art will readily recognize that magnetic junctions havingadditional and/or different layers not inconsistent with the method andsystem could also be used. Moreover, certain components are described asbeing magnetic, ferromagnetic, and ferrimagnetic. As used herein, theterm magnetic could include ferromagnetic, ferrimagnetic or likestructures. Thus, as used herein, the term “magnetic” or “ferromagnetic”includes, but is not limited to ferromagnets and ferrimagnets. Themethod and system are also described in the context of single magneticjunctions. However, one of ordinary skill in the art will readilyrecognize that the method and system are consistent with the use ofmagnetic memories having multiple magnetic junctions. Further, as usedherein, “in-plane” is substantially within or parallel to the plane ofone or more of the layers of a magnetic junction. Conversely,“perpendicular” corresponds to a direction that is substantiallyperpendicular to one or more of the layers of the magnetic junction.

FIG. 2 depicts an exemplary embodiment of a magnetic junction 100 aswell as surrounding structures. For clarity, FIG. 2 is not to scale.FIG. 3 depicts an embodiment of the magnetic junction 100 without thesurrounding structures. Referring to FIGS. 2-3, the magnetic junctionmay be used in a magnetic device such as a spin transfer torque randomaccess memory (STT-RAM) and, therefore, in a variety of electronicdevices. The magnetic junction 100 includes a pinned layer 110, anonmagnetic spacer layer 120, an asymmetric free layer 130 and aperpendicular magnetic anisotropy (PMA) inducing layer 140. Also shownin FIG. 2 is an underlying substrate 101 in which devices including butnot limited to a transistor may be formed. Although layers 110, 120, and130 are shown with a particular orientation with respect to thesubstrate 101, this orientation may vary in other embodiments. Forexample, in the embodiments shown in FIGS. 2-3, the magnetic junction100 is a top pinned layer junction. Thus, the free layer 130 is closerto the substrate 101 than the pinned layer 110. In other embodiments,the pinned layer 110 may be closer to the bottom (closest to thesubstrate 101) of the magnetic junction 100. Thus, the layers 110, 120,130 and 140 may be reversed in order in the perpendicular-to-plane (z)direction. Also shown are optional seed layer 104 and optional pinninglayer 106. The optional pinning layer 106 may be used to fix themagnetization (not shown) of the pinned layer 110. In some embodiments,the optional pinning layer 106 may be an AFM layer or multilayer thatpins the magnetization (not shown) of the pinned layer 110 by anexchange-bias interaction. However, in other embodiments, the optionalpinning layer 106 may be omitted or another structure may be used. Forexample, if the perpendicular magnetic anisotropy energy of the pinnedlayer 110 exceeds the out of plane demagnetization energy, the magneticmoment of the pinned layer 110 may be perpendicular to plane. In suchembodiments, the pinning layer 106 may be omitted. The magnetic junction100 is also configured to allow asymmetric the free layer 130 to beswitched between stable magnetic states when a write current is passedthrough the magnetic junction 100. Thus, the asymmetric free layer 130is switchable utilizing spin transfer torque. The magnetic junction 100may also include layers not shown in FIGS. 2-3. For example, magneticinsertion layer(s), sink layer(s) and/or other layer(s) may also bepresent.

The pinned layer 110 is magnetic and may have its magnetization pinned,or fixed, in a particular direction during at least a portion of theoperation of the magnetic junction. Although depicted as a simple layer,the pinned layer 110 may include multiple layers. For example, thepinned layer 110 may be a synthetic antiferromagnet (SAF) includingmagnetic layers antiferromagnetically or ferromagnetically coupledthrough thin layers, such as Ru. In such a SAF, multiple magnetic layersinterleaved with thin layer(s) of Ru or other material may be used. Thepinned layer 110 may also be another multilayer. Although amagnetization is not depicted in FIG. 2, the pinned layer 110 may have aperpendicular anisotropy energy that exceeds the out-of-planedemagnetization energy. Thus, as shown in FIG. 3, the pinned layer 110may have its magnetic moment oriented perpendicular to plane. Otherorientations of the magnetization of the pinned layer 110, including butnot limited to in-plane, are possible.

The spacer layer 120 is nonmagnetic. In some embodiments, the spacerlayer 120 is an insulator, for example a tunneling barrier. In suchembodiments, the spacer layer 120 may include crystalline MgO, which mayenhance the TMR of the magnetic junction as well as the perpendicularmagnetic anisotropy of the asymmetric free layer 130. For example, sucha tunneling barrier layer 120 may be at least eight Angstroms thick andnot more than twelve Angstroms thick. A crystalline MgO nonmagneticspacer layer 120 may also aid in providing a desired crystal structureand magnetic anisotropy for materials, such as CoFeB and FeB, in theasymmetric free layer 130. In alternate embodiments, the spacer layer120 may be a conductor, such as Cu or might have another structure, forexample a granular layer including conductive channels in an insulatingmatrix.

The asymmetric free layer 130 is magnetic and thermally stable atoperating temperatures. In some embodiments, therefore, the thermalstability coefficient, Δ, of the free layer 130 is at least sixty atoperating temperatures (e.g. at or somewhat above room temperature). Insome embodiments, the free layer 130 is a multilayer. The magneticjunction 100 is configured such that the asymmetric free layer 130 isswitchable between stable magnetic states when a write current is passedthrough the magnetic junction 100. For example, the magnetic junction100 may be switchable between stable states in which the magneticmoment(s) of the free layer 130 are oriented in the +z direction or the−z direction.

The asymmetric free layer 130 is asymmetric in theperpendicular-to-plane (z) direction. In particular, the boron contentof the free layer 130 varies in the perpendicular to plane direction.For example, the asymmetric free layer 130 may have a higher boroncontent closer to the substrate 101 and a lower boron content closer tothe pinned layer 110. Alternatively, the asymmetric free layer 130 mayhave a higher boron content closer to the pinned layer 110 and a lowerboron content closer to the substrate. Thus, in some embodiments, theboron concentration increases with increasing distance from the pinnedlayer 110. In other embodiments, the boron concentration decreases withincreasing distance from the pinned layer 110. In some embodiments, CoFeand/or Fe are the magnetic materials that are alloyed with boron in theasymmetric free layer 130. However, other magnetic materials might beused.

In some embodiments, this asymmetry in boron concentration is providedthrough the use of multiple layers. One such embodiment is depicted inFIG. 3. In this embodiment, the free layer 130 includes a low boroncontent ferromagnetic layer 132, an optional insertion layer 134 and ahigh boron content ferromagnetic layer 136. Both the ferromagnetic layer132 and 136 include B, but have differing concentrations of B. Forexample, the low boron content ferromagnetic layer 132 may include notmore than twenty atomic percent B. For example, the low boron contentferromagnetic layer 132 may be Fe_(1-x)B_(x), (CoFe)_(1-x)B_(x), where xis less than or equal to 0.2. Note that x may change throughout thelayer 132 as long as x does not exceed 0.2. The high boron content layer136 may have greater than twenty atomic percent boron. In someembodiments, the boron concentration of the ferromagnetic layer 136 isalso not more than fifty atomic percent. Thus, the high boron contentferromagnetic layer 136 may be Fe_(1-x)B_(x), (CoFe)_(1-x)B_(x), where xis less than or equal to 0.5 and greater than 0.2. In some embodiments,the high boron content ferromagnetic layer 136 includes at leasttwenty-five atomic percent and not more than forty five atomic percentboron. For example, the high boron content ferromagnetic layer 136 mayinclude at least thirty-five atomic percent and not more than forty fiveatomic percent boron. In such embodiments, therefore, the high boroncontent ferromagnetic layer 136 may be Fe_(1-x)B_(x), (CoFe)_(1-x)B_(x),where x is less than or equal to 0.45 and greater than or equal to 0.35.The concentration of boron may also vary within the layer 136 as long asit remains within the limits described above. In another embodiments,the boron concentration of the asymmetric free layer 130 may varysubstantially continuously and/or without clearly defined layers. TheCoFe in the layers 132 and 136 may be various stoichiometries includingbut not limited to 1:1 through 1:4. In some embodiments, the ratio of Feto Co is 3:1.

The free layer 130 may also include a nonmagnetic insertion layer 134,which is optional. The nonmagnetic insertion layer 134 includes at leastone of Bi, Ta, W, V, I, Zn, Nb, Ag, Cd, Hf, Os, Mo, Ca, Hg, Sc, Y, Sr,Mg, Ti, Ba, K, Na, Rb, Pb, and Zr in some embodiments. The nonmagneticinsertion layer 134 assists in ensuring that the perpendicular magneticanisotropy (PMA) of each of the ferromagnetic layers 132 and 136 exceedsthe out-of-plane demagnetization energy. Thus, the presence of thenonmagnetic insertion layer 134 aids in the use of thicker ferromagneticlayers 132 and 136 while preserving the perpendicular orientation of thestable states of the layers 132 and 136. In other embodiments, however,the insertion layer 134 may be omitted.

The thicknesses of the ferromagnetic layers 132 and 136 may be desiredto be thin in order to ensure the perpendicular magnetic anisotropy(PMA) exceeds the out-of-plane demagnetization energy for each of thelayers 132 and 136. Thus, as shown in FIG. 3, the magnetic moments ofthe layers 132 and 136 may be stable when oriented perpendicular toplane. If the nonmagnetic insertion layer 134 is omitted, then the freelayer 130 thickness (the thicknesses of both the layers 132 and 136combined) is desired to be not more than thirty Angstroms. If, however,the nonmagnetic insertion layer 134 is present, then the free layer 130may be thicker. In some embodiments, the free layer thickness may beless than thirty Angstroms. In some such embodiments, the free layerthickness does not exceed twenty Angstroms. For a free layer 130 havingits stable magnetic states with the magnetic moment orientedsubstantially perpendicular-to-plane, the layers 132 and 136 may each bedesired to be less than fifteen Angstroms thick. In some embodiments,the layers 132 and 136 are each not more than twelve Angstroms thick andat least three Angstroms thick. Further, the low boron concentrationlayer 132 may be desired to be thicker than the high boron content layer136. For example, the layer 136 may be nominally six Angstroms thick,while the layer 132 is nominally eight Angstroms thick. As a result, themagnetic moments of the layers 132 and 136 are stableperpendicular-to-plane.

The free layer 130 also includes a PMA inducing layer 140. The PMAinducing layer may be used to improve the PMA of the free layer 130. Forexample, the PMA inducing layer 140 may include an MgO layer that may beanalogous to the nonmagnetic spacer layer 120. However, the PMA inducinglayer 140 may be thinner than an MgO nonmagnetic spacer layer 120. Insome embodiments, the PMA inducing layer 140 may be at least fourAngstroms and not more than eight Angstroms.

The magnetic junction 100 may have enhanced magnetoresistance. This isbelieved to be due to the asymmetric concentration of boron in theasymmetric free layer 130. If the free layer 130 only included low boronconcentration (e.g. not more than twenty atomic percent), it is believedthat the tunneling magnetoresistance of the magnetic junction would bedepressed. However, the layer 136 may have a high boron concentration,as defined above, while the layer 132 may have a low boronconcentration. This gradient in boron concentration may result in anenhanced magnetoresistance for the magnetic junction 100. For example, atunneling magnetoresistance on the order of two hundred percent or moremay be achieved for a free layer including CoFeB in the layers 132 and136 and using MgO for the layers 120 and 140. It is believed that thehigh boron concentration, for example in the high boron content layer136, improves the crystallinity of the MgO layer 120 or 140 that isfurther from the substrate 101. This may be understood as follows.

Presume that the PMA layer 140 is deposited first and that layers 120and 140 are MgO. However, an analogous discussion may hold if thenonmagnetic spacer layer 120 is deposited first. The crystal structureof the first-deposited PMA layer 140 may affect the crystal structure ofthe second-deposited nonmagnetic spacer layer 120. If only lowerconcentrations of boron were present in a free layer, the later-formednonmagnetic spacer layer may not have the desired crystal structure.However, the free layer 130 has an asymmetric boron concentration. Thus,the free layer 130 may include the high content boron layer 136. It isbelieved that the higher boron concentration in the layer 136 blocks,mitigates, or delays the effect of the crystal structure of the PMAlayer 140 on the nonmagnetic spacer layer 120. As a result, thenonmagnetic spacer layer 120 is better allowed to crystallize with thedesired structure and orientation. For example, (001) MgO may be morelikely to be present in the nonmagnetic spacer layer 120 as well as thePMA layer 130. Consequently, the magnetoresistance of the magneticjunction 100 may be improved. Note that although this improvement isdiscussed within the context of a particular mechanism (e.g. boronconcentration of the free layer 130), the structures described hereinare not limited to functioning by this mechanism. Further, nothingprevents the structures described herein from use without theabove-described mechanism and/or benefits.

The magnetic junction 100 and asymmetric free layer 130 may haveimproved performance. The asymmetric free layer 130 may be switchedusing spin transfer torque. Thus, a more localized physical phenomenonmay be used to write to the magnetic junction 100. The magnetic junction100 may have stable magnetic states of the asymmetric free layer 130oriented perpendicular-to-plane, have an enhancedmagnetoresistance/tunneling magnetoresistance and improved spin transferbased switching. The PMA inducing layer 140 and a tunneling barrierlayer such as MgO for the nonmagnetic spacer layer 120 assist inensuring that the free layer magnetic moment(s) are orientedperpendicular-to-plane. The magnetic materials used in asymmetric freelayer 130/ferromagnetic layers 132 and 136 and the thicknesses of theasymmetric free layer 130/ferromagnetic layers 132 and 136 may also beconfigured such that the perpendicular-to-plane orientation of themagnetic moment(s) is achieved. The presence of the optional insertionlayer 134 may further assist in obtaining this magnetic orientation. Asa result, the spin transfer switching of the magnetic junction 100 maybe improved. Further, as discussed above, magnetoresistance of themagnetic junction 100 may be enhanced. Thus, performance of a deviceutilizing the magnetic junction 100 may be improved.

FIG. 4 depicts another exemplary embodiment of a magnetic junction 100′usable in a magnetic device. The magnetic device in which the magneticjunction 100′ is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 4 isnot to scale.

The magnetic junction 100′ is analogous to the magnetic junction 100.Consequently, analogous components are labeled similarly. The magneticjunction 100′ thus includes a pinned layer 110, a nonmagnetic spacerlayer 120, an asymmetric free layer 130 and a PMA inducing layer 140analogous to those depicted in FIGS. 2-3. The free layer 130 is alsoshown as including the low boron content ferromagnetic layer 132,optional insertion layer 134 and high boron content ferromagnetic layer136. Although layers 110, 120, 130 and 140 are shown with a particularorientation, this orientation may vary in other embodiments. Forexample, the pinned layer 110 may be closer to the bottom of themagnetic junction 100′ and the order of the layers 110, 120, 130 and 140may be reversed. Similarly, the layers 132, 134 and 136 are shown with aparticular orientation. In other embodiments, the orientation may vary.For example, the order of the layers 132, 134, and 136 may be reversedsuch that the layer 132 is closest to the PMA inducing layer 140. Themagnetic junction 100′ is also configured to allow the free layer 130 tobe switched between stable magnetic states when a write current ispassed through the magnetic junction 100′. Thus, the free layer 130 isswitchable utilizing spin transfer torque.

The structure and function of the layers 110, 120, 130, 132, 134, 136and 140 are analogous to those described above. For example, the freelayer 130 may have its magnetic moments oriented perpendicular-to-planewhen stable, as shown in FIG. 4, and has an asymmetric boronconcentration. The gradient in the boron concentration for the freelayer 130 and the layer(s) 132 and 136 is analogous to that discussedabove. In some embodiments, the layer 134 may be omitted.

The magnetic junction 100′ also includes a magnetic insertion layer 122between the nonmagnetic spacer layer 120 and the asymmetric free layer130. For example, the magnetic insertion layer may include at least oneof Fe and CoFe. In some embodiments, the insertion layer is an Fe layer.In some embodiments, the CoFe insertion layer is desired to have a Co toFe ratio of 1:3. In some embodiments, the magnetic insertion layer 122may be considered to be part of the free layer 130. The magneticinsertion layer 122 is generally desired to be thin. For example, themagnetic insertion layer 122 may be at least two Angstroms and not morethan six Angstroms thick. In some embodiments, the magnetic insertionlayer 122 is nominally four Angstroms thick. Use of the magneticinsertion layer may improve the magnetoresistance of the magneticjunction 100′.

The magnetic junction 100′ may have improved performance. The asymmetricfree layer 130 may be switched using spin transfer torque. Thus, a morelocalized physical phenomenon may be used to write to the magneticjunction 100′. The magnetic junction 100′ may have stable magneticstates of the asymmetric free layer 130 oriented perpendicular-to-plane,which may improve spin transfer based switching. The magnetic junction100′ may have an enhanced magnetoresistance/tunneling magnetoresistancethat may be due to the asymmetric free layer 130. Thus, performance of adevice utilizing the magnetic junction 100′ may be improved.

FIG. 5 depicts another exemplary embodiment of a magnetic junction 100″usable in a magnetic device. The magnetic device in which the magneticjunction 100″ is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 5 isnot to scale.

The magnetic junction 100″ is analogous to the magnetic junction(s) 100and/or 100′. Consequently, analogous components are labeled similarly.The magnetic junction 100″ thus includes a pinned layer 110, anonmagnetic spacer layer 120, an asymmetric free layer 130′ and a PMAinducing layer 140 analogous to the layers 120, 130 and 140 depicted inFIGS. 2-4. The free layer 130′ is also shown as including the low boroncontent ferromagnetic layer 132 and high boron content ferromagneticlayer 136. Although layers 110, 120, 130′ and 140 are shown with aparticular orientation, this orientation may vary in other embodiments.For example, the pinned layer 110 may be closer to the bottom of themagnetic junction 100″ and the order of the layers 110, 120, 130′ and140 may be reversed. Similarly, the layers 132 and 136 are shown with aparticular orientation. In other embodiments, the orientation may vary.For example, the order of the layers 132 and 136 may be reversed suchthat the layer 132 is closest to the PMA inducing layer 140. Themagnetic junction 100″ is also configured to allow the free layer 130′to be switched between stable magnetic states when a write current ispassed through the magnetic junction 100″. Thus, the free layer 130′ isswitchable utilizing spin transfer torque.

The structure and function of the layers 110, 120, 130′, 132, 136 and140 are analogous to those described above for the layers 110, 120, 130,132, 136 and 140, respectively. For example, the free layer 130′ mayhave its magnetic moments oriented perpendicular-to-plane when stable,as shown in FIG. 5, and has an asymmetric boron concentration. Thegradient in the boron concentration for the free layer 130′ and thelayer(s) 132 and 136 is analogous to that discussed above.

In the magnetic junction 100″, the nonmagnetic insertion layer isomitted from the free layer 130′. Thus, the layers 132 and 136 share aninterface. As a result, the free layer 130′ may be thinner in order toensure that the magnetic moment of the free layer 130′ isperpendicular-to-plane. For example, the sum of the thicknesses of thelayers 132 and 136 may be on the order of twelve Angstroms.

The magnetic junction 100″ may have improved performance. The asymmetricfree layer 130′ may be switched using spin transfer torque. Thus, a morelocalized physical phenomenon may be used to write to the magneticjunction 100″. The magnetic junction 100″ may have stable magneticstates of the asymmetric free layer 130′ orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 100″ may have an enhancedmagnetoresistance/tunneling magnetoresistance or reduced dampingconstant that may be due to the asymmetric free layer 130′. Thus,performance of a device utilizing the magnetic junction 100″ may beimproved.

FIG. 6 depicts another exemplary embodiment of a magnetic junction 100′″usable in a magnetic device. The magnetic device in which the magneticjunction 100′″ is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 6 isnot to scale.

The magnetic junction 100′″ is analogous to the magnetic junction(s)100, 100′ and/or 100″. Consequently, analogous components are labeledsimilarly. The magnetic junction 100′″ thus includes a pinned layer 110,a nonmagnetic spacer layer 120, an asymmetric free layer 130 and a PMAinducing layer 140 analogous to those depicted in FIGS. 2-5. The freelayer 130 is also shown as including the low boron content ferromagneticlayer 132, optional insertion layer 134 and high boron contentferromagnetic layer 136. Although layers 110, 120, 130 and 140 are shownwith a particular orientation, this orientation may vary in otherembodiments. For example, the pinned layer 110 may be closer to thebottom of the magnetic junction 100′″ and the order of the layers 110,120, 130 and 140 may be reversed. Similarly, the layers 132, 134 and 136are shown with a particular orientation. In other embodiments, theorientation may vary. For example, the order of the layers 132, 134, and136 may be reversed such that the layer 132 is closest to the PMAinducing layer 140. The magnetic junction 100′″ is also configured toallow the free layer 130 to be switched between stable magnetic stateswhen a write current is passed through the magnetic junction 100′″.Thus, the free layer 130 is switchable utilizing spin transfer torque.

The structure and function of the layers 110, 120, 130, 132, 134, 136and 140 are analogous to those described above. For example, the freelayer 130 may have its magnetic moments oriented perpendicular-to-planewhen stable, as shown in FIG. 6, and has an asymmetric boronconcentration. The gradient in the boron concentration for the freelayer 130 and the layer(s) 132 and 136 is analogous to that discussedabove. In some embodiments, the layer 134 may be omitted.

The magnetic junction 100′″ also includes a boron sink layer 142 suchthat the PMA induction layer 140 is between the boron sink layer 142 andthe free layer 130. In the embodiment shown, the boron sink layer 142also functions as a seed layer. However, in other embodiments, the boronsink layer 142 may be a capping layer, for example if the PMA layer 140is furthest from the bottom of the magnetic junction 100′″. The boronsink layer 142 may include material(s) that have an affinity for boron.For example, materials such as Ta, W, Fe, and/or CoFe may be used. Theboron sink layer 142 may provide a location to which boron may diffuseduring annealing or other processing of the magnetic junction 100′″.Thus, stoichiometry of the remaining layers 110, 120, 130 and 140 may becloser to that which is desired.

The magnetic junction 100′″ may have improved performance. Theasymmetric free layer 130 may be switched using spin transfer torque.Thus, a more localized physical phenomenon may be used to write to themagnetic junction 100′″. The magnetic junction 100′″ may have stablemagnetic states of the asymmetric free layer 130 orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 100′″ may have an enhancedmagnetoresistance/tunneling magnetoresistance that may be due to theasymmetric free layer 130. Thus, performance of a device utilizing themagnetic junction 100′″ may be improved.

FIG. 7 depicts another exemplary embodiment of a magnetic junction 100″″usable in a magnetic device. The magnetic device in which the magneticjunction 100″″ is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 7 isnot to scale.

The magnetic junction 100″″ is analogous to the magnetic junction(s)100, 100′, 100″ and/or 100′″. Consequently, analogous components arelabeled similarly. The magnetic junction 100″″ thus includes a pinnedlayer 110, a nonmagnetic spacer layer 120, an asymmetric free layer 130″and a PMA inducing layer 140 analogous to those depicted in FIGS. 2-6.The free layer 130″ is also shown as including the low boron contentferromagnetic layer 132, optional insertion layer 134 and high boroncontent ferromagnetic layer 136. Although layers 110, 120, 130″ and 140are shown with a particular orientation, this orientation may vary inother embodiments. For example, the pinned layer 110 may be closer tothe bottom of the magnetic junction 100′″ and the order of the layers110, 120, 130 and 140 may be reversed. The magnetic junction 100″″ isalso configured to allow the free layer 130″ to be switched betweenstable magnetic states when a write current is passed through themagnetic junction 100″″. Thus, the free layer 130″ is switchableutilizing spin transfer torque.

The structure and function of the layers 110, 120, 130″, 132, 134, 136and 140 are analogous to those described above. For example, the freelayer 130″ may have its magnetic moments oriented perpendicular-to-planewhen stable, as shown in FIG. 7, and has an asymmetric boronconcentration. The gradient in the boron concentration for the freelayer 130 and the layer(s) 132 and 136 is analogous to that discussedabove. However, in the embodiment shown, the order of the layers 132,134, and 136 has been reversed such that the layer 132 is closest to thePMA inducing layer 140. In some embodiments, the layer 134 may beomitted.

The magnetic junction 100″″ is also shown as including an optional boronsink layer 142 and an optional magnetic insertion layer 122. The layers122 and 142 are analogous to those discussed above. One or both of thelayers 122 and 142 may be included in the magnetic junction 100″″.Alternatively, one or both of the layers 122 and 142 may be omitted.

The magnetic junction 100″″ may have improved performance. Theasymmetric free layer 130″ may be switched using spin transfer torque.Thus, a more localized physical phenomenon may be used to write to themagnetic junction 100″″. The magnetic junction 100″″ may have stablemagnetic states of the asymmetric free layer 130″ orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 100″″ may have an enhancedmagnetoresistance/tunneling magnetoresistance that may be due to theasymmetric free layer 130″. Thus, performance of a device utilizing themagnetic junction 100″″ may be improved.

Note that FIGS. 2-7 have been described in the context of particularfeatures. For example, certain layers have been included or omitted invarious embodiments. However, one of ordinary skill in the art willrecognize that the one or more of the features in the embodiments 100,100′, 100″, 100′″ and/or 100″″ depicted in FIGS. 2-7 may be combined.

FIGS. 8-9 depict another exemplary embodiment of a magnetic junction 200usable in a magnetic device. FIG. 8 depicts the magnetic junction 200 aswell as surrounding structures. FIG. 9 depicts the magnetic junction 200without the surrounding structures and with a particular embodiment ofthe asymmetric free layer. The magnetic device in which the magneticjunction 200 is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIGS. 8 and9 are not to scale.

The magnetic junction 200 is analogous to the magnetic junctions 100,100′, 100″, 100′″ and/or 100″″. Consequently, analogous components arelabeled similarly. The magnetic junction 200 thus includes a pinnedlayer 210, a nonmagnetic spacer layer 220, an asymmetric free layer 230analogous to the layers 110, 120 and 130/130′/130″, respectively,depicted in FIGS. 2-7. The magnetic junction 200 also includes anadditional nonmagnetic spacer layer 240 and an additional pinned layer250. The additional nonmagnetic spacer layer 240 is analogous to thenonmagnetic spacer layer 120 as well as to the PMA inducing layer 140.The additional pinned layer 250 is analogous to the pinned layer110/210. Thus, the magnetic junction 200 is a dual magnetic junction.FIG. 8 also depicts a substrate 201, bottom contact 202, optional seedlayers 204, optional pinning layer 206 and top contact 203 that areanalogous to the substrate 101, bottom contact 102, optional seed layers104, optional pinning layer 106 and top contact 103, respectively. Themagnetic junction 200 also includes an optional pinning layer 260 thatis analogous to the optional pinning layer 206.

The free layer 230 is shown as including a low boron contentferromagnetic layer 232, optional insertion layer 234 and high boroncontent ferromagnetic layer 236 in FIG. 9. The low boron contentferromagnetic layer 232, optional insertion layer 234 and high boroncontent ferromagnetic layer 236 are analogous to the layers 132, 134 and136, respectively. The layers 232, 234 and 236 are shown with aparticular orientation. In other embodiments, the orientation may vary.For example, the order of the layers 232, 234, and 236 may be reversedsuch that the layer 232 is closest to the second nonmagnetic spacerlayer/PMA inducing layer 240. The magnetic junction 200 is alsoconfigured to allow the free layer 230 to be switched between stablemagnetic states when a write current is passed through the magneticjunction 200. Thus, the free layer 230 is switchable utilizing spintransfer torque.

The structure and function of the layers 210, 220, 230, 232, 234 and 236are analogous to those described above for layers 110, 120,130/130′/130″, 232, 234 and 236, respectively. For example, the freelayer 230 may have its magnetic moments oriented perpendicular-to-planewhen stable and has an asymmetric boron concentration. The gradient inthe boron concentration for the free layer 230 and the layer(s) 232 and236 is analogous to that discussed above for the layers 130/130′/130″,132 and 136, respectively. In some embodiments, the layer 234 may beomitted.

The pinned layers 210 and 250 are magnetic and may have theirmagnetizations pinned, or fixed, in a particular direction during atleast a portion of the operation of the magnetic junction. Althoughdepicted as a simple (single) layers, the pinned layer(s) 210 and/or 250may include multiple layers. For example, the pinned layer(s) 210 and/or250 may be SAF(s). The pinned layer(s) 210 and/or 250 may also beanother multilayer. As depicted in FIG. 9, the pinned layers 210 zand/or 250 may have a perpendicular anisotropy energy that exceeds theout-of-plane demagnetization energy. Thus, as shown in FIG. 9, thepinned layer(s) 210 and/or 250 may have its magnetic moment orientedperpendicular to plane. Other orientations of the magnetization of thepinned layer (s) 210 and/or 250, including but not limited to in-plane,are possible. The magnetic moments of the pinned layers 210 and 250 areshown as being antiparallel (in the dual state) However, in otherembodiments or during certain operations, the magnetic moments of thepinned layers 210 and 250 may be parallel. Such an orientation mayenhance magnetoresistance. In other embodiments, the orientations of themagnetic moments of the pinned layers 210 and 250 may be set differentlyfor read and write operations.

The spacer layers 220 and 240 are nonmagnetic. In some embodiments, thespacer layer(s) 220 and 240 may each an insulator, for example atunneling barrier. In such embodiments, the spacer layer(s) 220 and/or240 may include crystalline MgO, which may enhance the TMR of themagnetic junction as well as the perpendicular magnetic anisotropy ofthe asymmetric free layer 230. A crystalline MgO nonmagnetic spacerlayer 220 may also aid in providing a desired crystal structure andmagnetic anisotropy for materials, such as CoFeB and FeB, in theasymmetric free layer 230. In such embodiments, one or both of thelayers 220 and 240 may have a thickness of at least two and not morethan five Angstroms. In alternate embodiments, the spacer layer 120 maybe a conductor, such as Cu or might have another structure, for examplea granular layer including conductive channels in an insulating matrix.The nonmagnetic spacer layers 220 and 240 are generally desired to havedifferent thicknesses. For example, the thicknesses of the spacer layers220 and 240 may be ten percent different.

The magnetic junction 200 may have improved performance. The asymmetricfree layer 230 may be switched using spin transfer torque. Thus, a morelocalized physical phenomenon may be used to write to the magneticjunction 200. The magnetic junction 200 may have stable magnetic statesof the asymmetric free layer 230 oriented perpendicular-to-plane, whichmay improve spin transfer based switching. The magnetic junction 200 mayhave an enhanced magnetoresistance/tunneling magnetoresistance that maybe due to the asymmetric free layer 230. Thus, performance of a deviceutilizing the magnetic junction 200 may be improved.

FIG. 10 depicts another exemplary embodiment of a magnetic junction 200′usable in a magnetic device. The magnetic device in which the magneticjunction 200′ is used may be used in a variety of applications. Forexample, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 10 isnot to scale.

The dual magnetic junction 200′ is analogous to the dual magneticjunction 200. Consequently, analogous components are labeled similarly.The magnetic junction 200′ thus includes a pinned layer 210, anonmagnetic spacer layer 220, an asymmetric free layer 230, anonmagnetic spacer layer/PMA inducing layer 240 and pinned layer 250analogous to those depicted in FIGS. 8-9. The free layer 20 is alsoshown as including the low boron content ferromagnetic layer 232,optional insertion layer 234 and high boron content ferromagnetic layer236. The layers 232, 234 and 236 are shown with a particularorientation. In other embodiments, the orientation may vary. Forexample, the order of the layers 232, 234, and 236 may be reversed suchthat the layer 232 is closest to the nonmagnetic spacer layer/PMAinducing layer 240. The magnetic junction 200′ is also configured toallow the free layer 230 to be switched between stable magnetic stateswhen a write current is passed through the magnetic junction 200′. Thus,the free layer 230 is switchable utilizing spin transfer torque.

The structure and function of the layers 210, 220, 230, 232, 234, 236,240 and 250 are analogous to those described above. For example, thefree layer 230 may have its magnetic moments orientedperpendicular-to-plane when stable, as shown in FIG. 10, and has anasymmetric boron concentration. The gradient in the boron concentrationfor the free layer 230 and the layer(s) 232 and 236 is analogous to thatdiscussed above. In some embodiments, the layer 234 may be omitted.

The magnetic junction 200′ also includes magnetic insertion layer(s) 222and 241. The magnetic insertion layers 222 and 241 are analogous to thelayer 122 described in FIG. 4. Referring back to FIG. 10, one or both ofthe magnetic insertion layers 222 and 241 may be present. The magneticinsertion layers 222 and 241 may include at least one of Fe and CoFe.The magnetic insertion layers 222 and 241 may be desired to be Fe rich.For example an Fe layer or a Co₁Fe₃ layer might be used. In someembodiments, the magnetic insertion layer(s) 222 and/or 241 may beconsidered to be part of the free layer 230. The magnetic insertionlayers 222 and 241 are generally desired to be thin. For example, themagnetic insertion layers 222 and 241 may each be at least two Angstromsand not more than six Angstroms thick. In some embodiments, the magneticinsertion layers 222 and 241 are nominally four Angstroms thick. Use ofthe magnetic insertion layer may improve the magnetoresistance of themagnetic junction 200′.

The magnetic junction 200′ may have improved performance. The asymmetricfree layer 230 may be switched using spin transfer torque. Thus, a morelocalized physical phenomenon may be used to write to the magneticjunction 200′. The magnetic junction 200′ may have stable magneticstates of the asymmetric free layer 230 oriented perpendicular-to-plane,which may improve spin transfer based switching. The magnetic junction200′ may have an enhanced magnetoresistance/tunneling magnetoresistancethat may be due to the asymmetric free layer 230. Thus, performance of adevice utilizing the dual magnetic junction 200′ may be improved.

FIG. 11 depicts another exemplary embodiment of a dual magnetic junction200″ usable in a magnetic device. The magnetic device in which themagnetic junction 200″ is used may be used in a variety of applications.For example, the magnetic device, and thus the magnetic junction, may beused in a magnetic memory such as an STT-MRAM. For clarity, FIG. 11 isnot to scale.

The magnetic junction 200″ is analogous to the magnetic junction(s) 200and/or 200′. Consequently, analogous components are labeled similarly.The magnetic junction 200″ thus includes a pinned layer 210, anonmagnetic spacer layer 220, an asymmetric free layer 230′, anonmagnetic spacer/PMA inducing layer 240 and a pinned layer 250analogous to the layers 220, 230, 240 and 250 depicted in FIGS. 8-10.The free layer 230′ is also shown as including the low boron contentferromagnetic layer 232 and high boron content ferromagnetic layer 236.The layers 232 and 236 are shown with a particular orientation. In otherembodiments, the orientation may vary. For example, the order of thelayers 232 and 236 may be reversed such that the layer 232 is closest tothe nonmagnetic spacer/PMA inducing layer 240. The magnetic junction200″ is also configured to allow the free layer 230′ to be switchedbetween stable magnetic states when a write current is passed throughthe magnetic junction 200″. Thus, the free layer 230′ is switchableutilizing spin transfer torque.

The structure and function of the layers 210, 220, 230′, 232, 236, 240and 250 are analogous to those described above for the layers 210, 220,230, 232, 236, 240 and 250, respectively. For example, the free layer230′ may have its magnetic moments oriented perpendicular-to-plane whenstable, as shown in FIG. 11 and has an asymmetric boron concentration.The gradient in the boron concentration for the free layer 230′ and thelayer(s) 232 and 236 is analogous to that discussed above.

In the magnetic junction 200″, the nonmagnetic insertion layer isomitted from the free layer 230′. Thus, the layers 232 and 236 share aninterface. As a result, the free layer 230′ may be thinner in order toensure that the magnetic moment of the free layer 230′ isperpendicular-to-plane. For example, the sum of the thicknesses of thelayers 232 and 236 may be on the order of twelve Angstroms.

The magnetic junction 200″ may have improved performance. The asymmetricfree layer 230′ may be switched using spin transfer torque. Thus, a morelocalized physical phenomenon may be used to write to the magneticjunction 200″. The magnetic junction 200″ may have stable magneticstates of the asymmetric free layer 230′ orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 200″ may have an enhancedmagnetoresistance/tunneling magnetoresistance that may be due to theasymmetric free layer 230′. Thus, performance of a device utilizing themagnetic junction 200″ may be improved.

FIG. 12 depicts another exemplary embodiment of a magnetic junction200′″ usable in a magnetic device. The magnetic device in which themagnetic junction 200′″ is used may be used in a variety ofapplications. For example, the magnetic device, and thus the magneticjunction, may be used in a magnetic memory such as an STT-MRAM. Forclarity, FIG. 12 is not to scale.

The magnetic junction 200′″ is analogous to the magnetic junction(s)200, 200′ and/or 200″. Consequently, analogous components are labeledsimilarly. The magnetic junction 200′″ thus includes a pinned layer 210,a nonmagnetic spacer layer 220, an asymmetric free layer 230, anonmagnetic spacer/PMA inducing layer 240 and an additional pinned layer250 analogous to those depicted in FIGS. 8-11. The free layer 230 isalso shown as including the low boron content ferromagnetic layer 232,optional insertion layer 234 and high boron content ferromagnetic layer236. The layers 232, 234 and 236 are shown with a particularorientation. In other embodiments, the orientation may vary. Forexample, the order of the layers 232, 234, and 236 may be reversed suchthat the layer 232 is closest to the nonmagnetic spacer layer/PMAinducing layer 240. The magnetic junction 200′″ is also configured toallow the free layer 230 to be switched between stable magnetic stateswhen a write current is passed through the magnetic junction 200′″.Thus, the free layer 230 is switchable utilizing spin transfer torque.

The structure and function of the layers 210, 220, 230, 232, 234, 236,240 and 250 are analogous to those described above. For example, thefree layer 230 may have its magnetic moments orientedperpendicular-to-plane when stable, as shown in FIG. 12, and has anasymmetric boron concentration. The gradient in the boron concentrationfor the free layer 230 and the layer(s) 232 and 236 is analogous to thatdiscussed above. In some embodiments, the layer 234 may be omitted.

The magnetic junction 200′″ also includes a boron sink layer 242 suchthat the nonmagnetic spacer layer/PMA induction layer 240 is between theboron sink layer 242 and the free layer 230. The boron sink layer 242 isanalogous to the boron sink layer 142 depicted in FIG. 6. In theembodiment shown in FIG. 12, the boron sink layer 242 also functions asa seed layer. However, in other embodiments, the boron sink layer 242may be a capping layer, for example if the nonmagnetic spacer layer/PMAlayer 240 is furthest from the bottom of the magnetic junction 200′″.The boron sink layer 242 may include material(s) that have an affinityfor boron. For example, materials such as Ta, Fe, and/or CoFe may beused. The boron sink layer 242 may provide a location to which boron maydiffuse during annealing or other processing of the magnetic junction2200′″. Thus, stoichiometry of the remaining layers 210, 220, 230, 240and 250 may be closer to that which is desired.

The magnetic junction 200′″ may have improved performance. Theasymmetric free layer 230 may be switched using spin transfer torque.Thus, a more localized physical phenomenon may be used to write to themagnetic junction 200′″. The magnetic junction 200′″ may have stablemagnetic states of the asymmetric free layer 230 orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 200′″ may have an enhancedmagnetoresistance/tunneling magnetoresistance that may be due to theasymmetric free layer 230. Thus, performance of a device utilizing themagnetic junction 200′″ may be improved.

FIG. 13 depicts another exemplary embodiment of a dual magnetic junction200″″ usable in a magnetic device. The magnetic device in which themagnetic junction 200″″ is used may be used in a variety ofapplications. For example, the magnetic device, and thus the magneticjunction, may be used in a magnetic memory such as an STT-MRAM. Forclarity, FIG. 13 is not to scale.

The magnetic junction 200″″ is analogous to the magnetic junction(s)200, 200′, 200″ and/or 200′″. Consequently, analogous components arelabeled similarly. The magnetic junction 200″″ thus includes a pinnedlayer 210, a nonmagnetic spacer layer 220, an asymmetric free layer230″, a nonmagnetic spacer layer/PMA inducing layer 240 and anadditional pinned layer 250 analogous to those depicted in FIGS. 8-12.The free layer 230″ is also shown as including the low boron contentferromagnetic layer 232, optional insertion layer 234 and high boroncontent ferromagnetic layer 236. The magnetic junction 2100″″ is alsoconfigured to allow the free layer 230″ to be switched between stablemagnetic states when a write current is passed through the magneticjunction 200″″. Thus, the free layer 230″ is switchable utilizing spintransfer torque.

The structure and function of the layers 210, 220, 230″, 232, 234, 236,240 and 250 are analogous to those described above. For example, thefree layer 230″ may have its magnetic moments orientedperpendicular-to-plane when stable, as shown in FIG. 13, and has anasymmetric boron concentration. The gradient in the boron concentrationfor the free layer 230 and the layer(s) 232 and 236 is analogous to thatdiscussed above. However, in the embodiment shown, the order of thelayers 232, 234, and 236 has been reversed such that the layer 232 isclosest to the PMA inducing layer 240. In some embodiments, the layer234 may be omitted.

The magnetic junction 200″″ is also shown as including an optional boronsink layer 242 and an optional magnetic insertion layers 222 and 241.The layers 222, 241 and 242 are analogous to those discussed above. Somecombination of one or more of the layers 222, 241 and 242 may beincluded in the magnetic junction 200″″. Alternatively, one or more ofthe layers 222, 241 and 242 may be omitted.

The magnetic junction 200″″ may have improved performance. Theasymmetric free layer 230″ may be switched using spin transfer torque.Thus, a more localized physical phenomenon may be used to write to themagnetic junction 200″″. The magnetic junction 200″″ may have stablemagnetic states of the asymmetric free layer 230″ orientedperpendicular-to-plane, which may improve spin transfer based switching.The magnetic junction 200″″ may have an enhancedmagnetoresistance/tunneling magnetoresistance that may be due to theasymmetric free layer 230″. Thus, performance of a device utilizing themagnetic junction 200″″ may be improved.

Note that FIGS. 8-13 have been described in the context of particularfeatures. For example, certain layers have been included or omitted invarious embodiments. However, one of ordinary skill in the art willrecognize that the one or more of the features in the embodiments 200,200′, 200″, 200′″ and/or 200″″ depicted in FIGS. 8-13 may be combined.

FIG. 14 depicts an exemplary embodiment of a memory 300 that may use oneor more of the magnetic junctions 100, 100′, 100″, 100′″, 100″″, 200,200′, 200″, 200′″ and/or 200″″. Note, however, that one or more of themagnetic junctions 100, 100′, 100″, 100′″, 100″″, 200, 200′, 200″, 200′″and/or 200″″ might be used in a different device and/or a memory havinga different configuration. The magnetic memory 300 includesreading/writing column select drivers 302 and 306 as well as word lineselect driver 304. Other and/or different components may be provided.The storage region of the memory 300 includes magnetic storage cells310. Each magnetic storage cell includes at least one magnetic junction312 and at least one selection device 314. In some embodiments, theselection device 314 is a transistor. The magnetic junction(s) 312 maybe one of the magnetic junctions 100, 100′, 100″, 100′″, 100″″, 200,200′, 200″, 200′″ and/or 200″″ disclosed herein. Thus, the free layersof the magnetic junctions 312 is asymmetric. Although one magneticjunction 312 is shown per cell 310, in other embodiments, another numberof magnetic junctions 312 may be provided per cell. As such, themagnetic memory 300 may enjoy the benefits described above.

FIG. 15 depicts an exemplary embodiment of a method 400 for fabricatingmagnetic junction. For simplicity, some steps may be omitted orcombined. The method 400 is described in the context of the magneticjunction 100. The method 400 may also be used in fabricating one or moreof the magnetic junctions 100′, 100″, 100′″, 100″″, 200, 200′, 200″,200′″ and/or 200″″. The method 400 may be used on other magneticjunctions. Further, the method 400 may be incorporated into fabricationof magnetic memories. Thus the method 400 may be used in manufacturing aSTT-MRAM or other magnetic memory.

The pinned layer 110 is provided, via step 402. Step 402 may includedepositing the desired materials at the desired thickness of the pinnedlayer 110. The nonmagnetic layer 120 is provided, via step 404. Step 404may include depositing the desired nonmagnetic materials. For example,MgO may be deposited. In addition, the desired thickness of material maybe deposited in step 404. The asymmetric free layer 130 is provided, viastep 406. Step 406 may include providing layers 132, 134 and 136. Inother embodiments, a single layer having a substantially continuousvariation in the boron concentration may be provided. The PMA inducinglayer 140 is provided, via step 408. If a dual magnetic junction such asthe junction 200, 200′, 200″, 200′″ and/or 200″″ is provided, then thelayer provided in step 308 is also a nonmagnetic spacer layer for thedual junction. The pinning layer 250 may optionally be provided, viastep 410. Fabricating of the magnetic junction 100 may then becompleted, via step 412. Consequently, the benefits of the magneticjunction(s) 100, 100′, 100″, 100′″, 100″″, 200, 200′, 200″, 200′″ and/or200″″ may be achieved.

A method and system for providing a magnetic junction and a memoryfabricated using the magnetic junction has been described. The methodand system have been described in accordance with the exemplaryembodiments shown, and one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments, and anyvariations would be within the spirit and scope of the method andsystem. Accordingly, many modifications may be made by one of ordinaryskill in the art without departing from the spirit and scope of theappended claims.

We claim:
 1. A magnetic junction for use in a magnetic devicecomprising: a pinned layer; a nonmagnetic spacer layer; an asymmetricfree layer, the nonmagnetic spacer layer residing between the pinnedlayer and the asymmetric free layer, the asymmetric free layer includinga first ferromagnetic layer having a first boron content and a secondferromagnetic layer having a second boron content, the second boroncontent being less than the first boron content, the first boron contentand the second boron content being greater than zero atomic percent; anda perpendicular magnetic anisotropy (PMA) inducing layer, the free layerbeing between the PMA inducing layer and the asymmetric free layer;wherein the magnetic junction is configured such that the asymmetricfree layer is switchable between a plurality of stable magnetic stateswhen a write current is passed through the magnetic junction.
 2. Themagnetic junction of claim 1 wherein the free layer further includes anonmagnetic insertion layer between the first ferromagnetic layer andthe second ferromagnetic layer.
 3. The magnetic junction of claim 2wherein the nonmagnetic insertion layer includes at least one of Bi, Ta,W, V, I, Zn, Nb, Ag, Cd, Hf, Os, Mo, Ca, Hg, Sc, Y, Sr, Mg, Ti, Ba, K,Na, Rb, Pb, and Zr.
 4. The magnetic junction of claim 1 wherein thefirst boron content is at greater than twenty atomic percent and lessthan fifty atomic percent and wherein the second boron content is notmore than twenty atomic percent.
 5. The magnetic junction of claim 4wherein the first boron content is at least twenty-five atomic percentand not more than forty-five atomic percent.
 6. The magnetic junction ofclaim 5 wherein first ferromagnetic layer and the second ferromagneticlayer each contain at least one of Co and Co Fe.
 7. The magneticjunction of claim 1 wherein the second ferromagnetic layer is betweenthe first ferromagnetic layer and the pinned layer.
 8. The magneticjunction of claim 1 further comprising: a magnetic insertion layerbetween the nonmagnetic spacer layer and the free layer.
 9. The magneticjunction of claim 1 further comprising: a boron sink layer, the PMAinducing layer being between the free layer and the boron sink layer.10. The magnetic junction of claim 1 wherein the nonmagnetic spacerlayer and the PMA inducing layer each include MgO.
 11. The magneticjunction of claim 1 further comprising: an additional pinned layer, thePMA inducing layer residing between the free layer and the additionalpinned layer, the PMA inducing layer being a nonmagnetic spacer layer.12. A magnetic device including a magnetic memory and comprising: aplurality of magnetic storage cells for the magnetic memory, each of theplurality of magnetic storage cells including at least one magneticjunction, each of the at least one magnetic junction including a pinnedlayer, a nonmagnetic spacer layer, an asymmetric free layer, and aperpendicular magnetic anisotropy (PMA) inducing layer, the nonmagneticspacer layer being between the free layer and the pinned layer, the freelayer being between the nonmagnetic spacer layer and the PMA inducinglayer, the asymmetric free layer including a first ferromagnetic layerhaving a first boron content and a second ferromagnetic layer having asecond boron content, the second boron content being less than the firstboron content, the first boron content and the second boron contentbeing greater than zero atomic percent, the magnetic junction beingconfigured such that the asymmetric free layer is switchable between aplurality of stable magnetic states when a write current is passedthrough the magnetic junction; and a plurality of bit lines coupled withthe plurality of magnetic storage cells.
 13. The magnetic memory ofclaim 12 wherein the free layer further includes a nonmagnetic insertionlayer between the first ferromagnetic layer and the second ferromagneticlayer.
 14. The magnetic memory of claim 13 wherein the nonmagneticinsertion layer includes at least one of Bi, Ta, W, V, I, Zn, Nb, Ag,Cd, Hf, Os, Mo, Ca, Hg, Sc, Y, Sr, Mg, Ti, Ba, K, Na, Rb, Pb, and Zr.15. The magnetic memory of claim 12 wherein the first boron content isat greater than twenty-five atomic percent and less than forty-fiveatomic percent and wherein the second boron content is not more thantwenty atomic percent.
 16. The magnetic memory of claim 12 wherein firstferromagnetic layer and the second ferromagnetic layer each contain atleast one of Co and CoFe.
 17. The magnetic memory of claim 12 whereinthe second ferromagnetic layer is between the first ferromagnetic layerand the pinned layer.
 18. The magnetic memory of claim 12 wherein eachof the at least one magnetic junction further includes at least one of amagnetic insertion layer and a boron sink layer, the magnetic insertionlayer being between the nonmagnetic spacer layer and the free layer, thePMA inducing layer being between the free layer and the boron sinklayer.
 19. The magnetic memory of claim 12 wherein each of the at leastone magnetic junction further includes an additional pinned layer, thePMA inducing layer residing between the free layer and the additionalpinned layer, the PMA inducing layer being a nonmagnetic spacer layer.20. A method for providing a magnetic junction for use in a magneticdevice comprising: providing a pinned layer; providing a nonmagneticspacer layer; providing an asymmetric free layer, the nonmagnetic spacerlayer residing between the pinned layer and the asymmetric free layer,the asymmetric free layer including a first ferromagnetic layer having afirst boron content and a second ferromagnetic layer having a secondboron content, the second boron content being less than the first boroncontent, the first boron content and the second boron content beinggreater than zero atomic percent; and providing a perpendicular magneticanisotropy (PMA) inducing layer, the free layer being between the PMAinducing layer and the asymmetric free layer; wherein the magneticjunction is configured such that the asymmetric free layer is switchablebetween a plurality of stable magnetic states when a write current ispassed through the magnetic junction.